Amorphous resins, such as polymethyl methacrylate (referred to as PMMA hereinafter) or polycarbonate (referred to as PC hereinafter), have been widely used in the art in optical materials and in individual components of domestic electrical appliances, office equipment, automobiles, and so on, since they have high transparency and dimensional stability.
In recent years, these resins have been widely used as optical materials having higher performance, especially, for optical lenses, prisms, mirrors, optical discs, optical fibers, sheets or films for liquid crystal displays, light transmission plates, or the like. Therefore, the required optical properties, moldability and heat resistance of the resin must to be high.
Furthermore, at present these transparent resins are also used as lighting fixtures in automobiles or the like, such as tail lamps and headlamps. In recent years, in order to increase the space in automobiles or improve fuel consumption, there has been a trend to reduce the space between light sources and various lenses, such as tail lamps, inner lenses, headlamps, shield beams or the like, and to reduce the thickness of various parts, and excellent moldability is required. Further, since automobiles are used in extreme conditions, little change in shape at high temperature and humidity, and excellent scratch resistance, weatherability, and oil resistance are also required.
However, although the PMMA resin has excellent transparency and weatherability, this resin has problems in that the heat resistance and impact resistance are insufficient. On the other hand, although the PC resin has excellent heat resistance and impact resistance, this resin has problems in that a birefringence, which is optical strain, is large, thus generating optical anisotropy in the molded product, and the moldability, scratch resistance and solvent resistance are substantially lower.
Therefore, in order to improve the heat resistance of PMMA, resins having a maleimide monomer, a maleic anhydride monomer, or the like introduced as a component giving heat resistance have been developed. However, a problem with the maleimide monomer is that the cost is high and reactivity is low, and a problem with the maleic anhydride monomer is that the thermal stability is insufficient.
As a method for solving such problems, a copolymer containing a glutaric anhydride-containing component was disclosed in GB1437176A and EP0306133A, wherein the component is obtained by heating a copolymer containing an unsaturated carboxylic acid monomer component by using an extruder and carrying out a cyclizing reaction. Furthermore, as a method for improving the mechanical properties such as the impact resistance or the like, a method was disclosed in JP60-67557A, JP60-120734A, JP4-277546A and JP5-186659A wherein a rubber-containing polymer compound is added to a copolymer containing the unsaturated carboxylic acid monomer component. However, in the methods disclosed in these patent documents, although the mechanical properties such as the impact resistance can be improved, there are problems in that the transparency of the resin composition is remarkably decreased and a stress optical coefficient (birefringence), that is optical anisotropy, is increased. No material having sufficient mechanical properties such as impact resistance and; good optical properties (transparency, optical isotropy), which have been required in recent years have not yet been known.
It would therefore be advantageous to provide a thermoplastic resin composition having high heat resistance and mechanical properties, high colorless transparency, optical isotropy and moldability (flowability), which have been required in recent years, and also having solvent resistance.